1. Field of the Invention
This invention relates to back flow preventer valves, and more particularly, to in-line back flow preventer valves of the reduced pressure zone type for liquid systems.
2. Description of the Prior Art
In industrial and residential water supply lines, back flow of contaminated water into the supply lines presents problems under variable water pressure conditions. Because this problem particularly affects the health of communities, there are established criterion for the design and performance of back flow preventer valves. These performance requirements are described in the American Society of Sanitary Engineering Standard No. 1013 issued June 1971, and also in the Manual of Cross-Connection Control published by the Foundation for Cross-Connection and Hydraulic Research.
When used herein, "back flow" means and includes both "back pressure back flow" which is a reversal of the normal direction of flow in the pipeline due to a condition which causes the pressure in the system being supplied to become greater than that in the supply line, the system pressure being always above atmospheric; and "back siphonage back flow" which is a reversal of the normal direction of flow in the pipeline due to a negative pressure (vacuum) being created in a supply line with the back flow source subject to atmospheric or higher pressure.
In contending with the back flow problem, many back flow preventer valves have been proposed and used with the design based primarily on conventional valving systems including springs, stems associated with the springs, diaphragms and circular surfaced mating valve seals. Exemplary of such devices are those shown in U.S. Pat. Nos. 2,372,940; 2,491,604; 3,114,382; 3,173,439; 3,286,722; 3,636,968; 3,724,487; 3,747,621; 3,868,962; 3,905,382; and 3,906,987. In addition to those back flow preventer valves there are one way valves and check valves which use similar structures as flow restricting means under flow reversal conditions. Exemplary of such valves are those shown in U.S. Pat. Nos. 2,746,477 and 2,620,816. Further, elastomeric check valves have been proposed which involve the mating of elastomeric surfaces utilizing their deformable characteristics. Exemplary of such check valves are U.S. Pat. Nos. 2,328,382; 2,270,737; and 3,952,766.
Another problem associated with back flow preventer valves is related to their maintenance and access. The several mechanical parts including springs, seals, etc., require excessive maintenance time in replacing worn or damaged parts. During the normal course of valve operation those parts which are subject to wear, such as valve stems, valve seats and springs, must be replaced at certain intervals to insure effectiveness of the back flow valve.
In accordance with the present invention, a back flow preventer valve is provided which uses no mechanically moving parts, such as springs and valve stems, and is easily assembled and disassembled for the replacement of parts worn during the normal course of operation. In addition, the present invention provides a back flow preventer which permits easy access to the internal parts thereof without the necessity of removing the device from the pipeline or disassembling the pipeline.
Further in accordance with the present invention, a back flow preventer valve is provided with a minimal number of parts in an uncomplicated arrangement which minimizes the chance for malfunction of the device.